The development, deployment and refinement of wireless communication systems and devices have increased dramatically over recent years. Indeed, the cellular telephone, which was an expensive and awkward device to use just a couple of decades ago, has become commonplace in today's world. Communicating wirelessly is desirable since it allows user mobility and provides a user, in most respects, the ability to establish communications with another user irrespective of knowledge of the other user's location.
The prospect that the mobile nature of wireless communications would extend from just voice communications to data communications was inevitable. Indeed, wireless data communications between portable computers and other portable devices (e.g. laptop computers and personal digital assistants (PDAs)) has become one of the fastest growing technology areas.
A number of approaches have been proposed and developed to support the demand for wireless data communications. A popular one of these approaches involves the use of a PC Card wireless modem (also referred to as a wireless “network interface card” or wireless “NIC”), which functions as an interface between a portable data communications device (e.g. a laptop computer or PDA) and a wireless wide area network (e.g. a cellular wireless network). A PC Card is a peripheral device, which conforms to standards (e.g. electrical specifications and form factor requirements) set by the PCMCIA (Personal Computer Memory Card International Association). Although originally formed to formulate standards relating to adding memory to portable computers, the PCMCIA standard has been expanded several times and is now applicable to many types of devices, including PC card wireless modems.
A PC Card wireless modem is about the size of a credit card and plugs into a PCMCIA slot of a portable communications device. FIG. 1 shows a conceptual diagram of a laptop computer 10 with a PC Card wireless modem 12 plugged into a PCMCIA slot 14 of the laptop computer 10. Similar to a cellular telephone, the PC Card wireless modem 12 includes an antenna 16 for receiving radio frequency RF signals from a remote device over a wide area network. The dimensions of the antenna 16 are set so that the antenna 16 can properly receive RF signals within a frequency band, e.g. as may be defined by a particular wireless technology standard. For example, as shown in FIG. 2, the antenna 16 may be dimensioned so that it is capable of receiving PCS band (1.92 GHz) frequencies. While this is beneficial, the fixed dimensions of the antenna 16 limit the PC Card wireless modem's reception capabilities to only PCS band signals. In other words, the fixed dimensions of the antenna restrict the use of the PC Card wireless modem to a single wireless technology. FIG. 2 illustrates this limitation imposed on a PC Card wireless modem having an antenna 16 configured to receive 1.92 GHz PCS band signals. While the antenna 16 is capable of receiving signals from within the 1.92 GHz PCS band, its dimensions are too small to properly receive CDMA 0.86 GHz band (i.e. CDMA800) signals.
It would be desirable, therefore, to have an antenna system for a PC Card wireless modem, or equivalent device, capable of properly receiving RF signals from more than a single frequency band and/or capable of receiving RF signals from wireless networks defined by competing wireless technologies.